Neoclerodane diterpenoids from Scutellaria barbata with cytotoxic activities

Two new neoclerodane diterpenoids, barbatin F (1), barbatin G (2) together with four known compounds, scutebata A (3), scutebata B (4), scutebata C (5) and scutebata P (6) were isolated from the whole plant of Scutellaria barbata D.Don. Their structures were elucidated on the basis of spectroscopic studies. In vitro cytotoxicity of selected compounds against cancer cell lines LoVo, SMMC-7721, HCT-116, and MCF-7 were evaluated, compound 1 and 2 showed weak cytotoxic activities against HCT-116 colon cancer cell lines with IC₅₀ value of 44.3, 32.3 μM, respectively, while compound 3 and 4 exhibited moderate cytotoxic activities against four tested human cancer cell lines with IC₅₀ values of 5.31～28.5 μM.